This invention relates to a control system for a hydraulically operated excavator thumb and a method of controlling the excavator thumb.
Construction equipment is used to perform a variety of tasks on construction sites, demolition sites, in scrap yards, in road work, in mines, in railroad maintenance, and in other applications. Versatility is often an important feature to a person using such equipment. Construction equipment used in these areas includes excavators, backhoes, and other well-known pieces of equipment. With respect to excavators and backhoes, a common configuration comprises a tractor portion carrying a boom which in turn carries a stick. The stick carries any of several implements. One common implement is a bucket used in excavating. An operator sits on the tractor portion of the backhoe or excavator and uses control levers to control various hydraulic cylinders moving the boom, stick and bucket. In this configuration, the excavator or backhoe is used to excavate holes, trenches and the like. Some object lifting can be done in this configuration by picking up an object in the bucket or by attaching an object to the bucket by means of chains or the like.
Some operators of excavators and backhoes attach a thumb to the stick. The thumb is controlled by a hydraulic cylinder allowing the thumb to be pivoted around an attachment point to close against the excavator bucket. This allows one to position the bucket against a workpiece to be lifted and close the thumb against the workpiece. The workpiece is held and moved as desired by moving the boom and stick. The thumb holds the workpiece against the bucket as a person""s thumb can hold an object against the palm of the hand. While this thumb arrangement has advantages, it also has significant limitations. If one moves the bucket away from the thumb while engaged to a workpiece, the piece may be dropped. Moving the bucket and thumb together with the workpiece retained is not easy. The geometry of how the cylinders work on the bucket and the thumb are often different. If the cylinders are both extended the same amount, the thumb may move a different angular distance than the bucket. Moreover, this geometry sometimes changes over the stroke of the cylinders. Additionally, the diameter of the bucket cylinder and thumb cylinder are often different. Therefore the cylinders may extend or retract at different rates given the same flow of hydraulic fluid. Thus, the conventional control systems for a thumb and bucket used on an excavator are far from ideal.
In accordance with the present invention, there is provided a control system for an excavator thumb in which a thumb close switch is depressed causing a hydraulic fluid at a select close pressure to be applied to the cylinder closing the thumb. This select close pressure is automatically maintained closing the thumb against the bucket or a workpiece.
Further in accordance with the invention, the thumb close switch is latched so that the selected closed pressure will be maintained until a thumb open switch is activated.
Still further in accordance with the invention, a thumb control circuit is provided for an excavator in which a thumb is mounted opposable to a bucket and controlled by a thumb cylinder. The thumb cylinder is actuated by a latching switch in the close direction and a non-latching switch in the open direction which switches control valves directing fluid to the thumb cylinder. Fluid directed to the thumb cylinder when the close switch is latched is passes through a pressure reducing valve delivering fluid at a selected lower pressure and maintaining this pressure until the close switch is unlatched.
Still further in accordance with the invention, a control for a thumb on an excavator is provided with bypass valves allowing one to remove the thumb and use the hydraulic circuits otherwise controlling the thumb in other applications, such as driving an impact hammer.
Still further in accordance with the invention, a control for a hydraulic thumb on an excavator is provided requiring operator input only to change state.
It is the principal object of the present invention to provide a control system for an excavator thumb which is robust, easy to use, versatile, and easily installed.
It is another object of the present invention to provide a control for an excavator thumb which will automatically close upon a workpiece at the press of a button.
It is yet another object of the present invention to provide a control system for an excavator thumb which will close upon a workpiece using a preset reduced fluid pressure and maintain this pressure until disengaged by the operator.
It is still another object of the present invention to provide a control system for a thumb on an excavator which will hold the workpiece against the bucket using a selected cylinder fluid close pressure and maintain this pressure when an operator moves the bucket.
It is still another object of the present invention to provide a control system for an excavator thumb including bypasses allowing one to use the hydraulic circuit for implements other than the thumb without removal of the thumb control mechanism.
It is still another object of the present invention to provide a control system for an excavator thumb in which the thumb can be disengaged from a workpiece and easily moved to a desired disengaged position.
It is still another object of the present invention to provide a control system for an excavator thumb in which the thumb, when activated, will hold a workpiece against the bucket and follow the bucket through curl and uncurl movements.
It is yet another object of the present invention to provide a thumb control circuit which is inexpensive, easy to install, easy to use and uses existing excavator control components.
It is yet another object of the present invention to provide a control system for an excavator thumb using electrical switches in the operator cab to control the thumb thereby easing installation.
It is yet another object of the present invention to provide a method of controlling a thumb on an excavator allowing an operator to easily grasp a workpiece between a bucket and the thumb and maintain a positive grip on the workpiece automatically during manipulation of the bucket.
It is yet another object of the present invention to provide a method of controlling an excavator thumb which is automatic.
It is still another object of the present invention to provide a method for controlling a thumb which is easy to use in that once the thumb is engaged, operator control becomes unnecessary.
It is another object of the present invention to provide a method of controlling an excavator thumb which is easily disengaged allowing an operator to positively position the thumb in a disengaged position.
It is yet another object of the present invention to provide a control system for an excavator thumb which is easily maintained in the field, robust, not prone to failure, and has only minimal moving parts.